Real navigation target motion analysis cheatsheet

[palmic]

Read legend at those tables carefully.
Tangent values are from left top, contangent values are from bottom right to top left (in opaque way).

[palmic]

Originally Posted by hauangua

I download your tables... but no see 0.661 ...Ctg of 56.4...!!
this I no understand

[hauangua]

Originally Posted by palmic

Thanks...
me and mathematic...no good feeling

[palmic]

You're welcome, try it and you'll not be regret it

BTW. you could be pretty comfortable to use 0.7 here, dont be very hard for yourself in this calculations as you cant get even those hydrophone bearing so precised..
And dont even push yourself to measure it in too perfect time, just feel free to have 2. bearing after 9:30 and third after 11 it doesnt matter so much.... (just dont mess it by 30% or so...)

In the end you always have to get more precise information optically from periscope anyway.
This is rather for decide good approach strategy and to know which bearing to have roughly before fire to not to have to turn ubote later..

[Unkki]

Thanks for the videos!

I see in the video you can move an earlier made line by clicking it. I can't do this? Do I need to press a button or something?

Thanks !

[Xall]

Hey palmic, I been trying to understand your methods, I been reading this one and trying to understand it, and I get stuck on one point, I am hoping you can help me with it.

So I will recap and show you how far I get.

First we have our course of 255 and our 3 bearings,

b1 = 71
b2 = 80
b3 = 87

each timed at 10 minutes in this case, while we are stationary.

Next we use your cheatsheet to find the cotangents,

cotan for b1 to b2 is 9 so we get = 6.3138 from your sheet,
and
cotan for b1 to b3 is 16 so we get 3.4874

so far so good.

next we have the formula

and this is where I cannot find out what the DRM is, direction of relative motion, is that not the angle beween our course and the target course? If so, how do we find the target course?

How do we find this?



----------------------------------------------------------------------------------------------------------------------



EDIT: I just read the conversation between you and hauangua, seems like he ran into the same confussion,

So what I understand is that, once you do the formula,
Cot(DRM -B1) = 2* Cot13 -Cot12 = 0.661

Then we Search in the cheatsheet for the closest value?
So in the Cheatsheet the closest value in this case is = 0.6644?

So 0.661 becomes 0.6644 which is = 56?

Am I understanding this correctly?

[Cyborg322]

HI Palmic

I overlooked your Tables they are very good , Odd description "Cheatsheet" its definitely not a cheat its just good Maths was this method Actually used by the Kriegsmarine ? Would be interested to know.

THX Best Regards Simon

WOLVES OF STEEL MEGAMOD

[palmic]

Originally Posted by Xall

Hey palmic, I been trying to understand your methods, I been reading this one and trying to understand it, and I get stuck on one point, I am hoping you can help me with it.

So I will recap and show you how far I get.

First we have our course of 255 and our 3 bearings,

b1 = 71
b2 = 80
b3 = 87

each timed at 10 minutes in this case, while we are stationary.

Next we use your cheatsheet to find the cotangents,

cotan for b1 to b2 is 9 so we get = 6.3138 from your sheet,
and
cotan for b1 to b3 is 16 so we get 3.4874

so far so good.

next we have the formula

and this is where I cannot find out what the DRM is, direction of relative motion, is that not the angle beween our course and the target course? If so, how do we find the target course?

How do we find this?



----------------------------------------------------------------------------------------------------------------------



EDIT: I just read the conversation between you and hauangua, seems like he ran into the same confussion,

So what I understand is that, once you do the formula,
Cot(DRM -B1) = 2* Cot13 -Cot12 = 0.661

Then we Search in the cheatsheet for the closest value?
So in the Cheatsheet the closest value in this case is = 0.6644?

So 0.661 becomes 0.6644 which is = 56?

Am I understanding this correctly?

Hi Xall!
Sorry for my delay, i noticed right now.

Yes you have it right. Your targets DRM is 56.
Now you just have to subtract, or add it to first ABSOLUTE bearing.
Since your course in that time was 255 and the first bearing was 71, absolute bearing was 255+71=326.
Since bearings went up, you have to add, you would subtract otherwise.
So course of your target is 326+56=382=22!

For educative details about DRM please read the document from my initial post.

Just one more thing, you are unnecessarily too exact, round just to 1 decimal, your bearings from hydrophone and timing is the same unexact anyway and youll be surprised how exactly youll calculate even with one dec, its just way more quicker..

Happy hunting!

[palmic]

Originally Posted by Cyborg322

HI Palmic

I overlooked your Tables they are very good , Odd description "Cheatsheet" its definitely not a cheat its just good Maths was this method Actually used by the Kriegsmarine ? Would be interested to know.

THX Best Regards Simon

WOLVES OF STEEL MEGAMOD

Hi Cyborg322, its like cheatsheat in school because it keeps my shortcuts for getting the sollution

I would bet they've used this, but they used just very rounded way how to getting these informations and they did just easier math in head i think..
They just remembered cotangents of most common angles rounded to 1 decimal point, thats enough even here to get good enough solution. I use it like this.

[McDonnel]

I am sorry to resurrect this old thread, but I would really like some help here with the target course determination.

Let me use my example, encountered in the game - "stationary" 4-bearings method, readings taken at the same time interval of 10 minutes:

Co = 287° (my u-boot course)
b1 = 48°
b2 = 59°
b3 = 70°

So, if I start calculation using the easiest formula:
1) Cot(DRM - B1) = 2*Cot (22) - Cot(11)
2) Cot(DRM - B1) = 2*2,4751 - 5,1446
3) Cot(DRM - B1) = 4,9502 - 5,1446
4) Cot(DRM - B1) = -0,1944 (this is negative, so I take absolute value, determine angle of 79 from the tables provided and put it further as (90-79+90 = 101) according to your instructions)
5) DRM - B1 = 101 degrees
6) DRM = 149 degrees (correct? or do I use here the true bearing of b1t = 335° (= Co + b1 = 287+48) already, which gives different DRM = 436 (-360?) = 76 degrees?)

How do I get from here to the target course?
Ct = Co + DRM according to your instructions, but no matter if I use 149 or 76, (resulting in either Ct = 287+149 (-360) = 76° (??) or Ct = 287 + 76 (-360) = 3°

For the Poseidon´s beard, I am unable to get to that correct target course of cca 91°, which I get with graphic resolution.

Thank you very much for any help.

Btw: Spiess line formula comes out to 80,24°, which is pretty close to expected 81° (and later verified 82° from graphic solution).

[palmic]

Hi McDonnel,
Your target course is 76.

Funny thing is how i shortened the calculation in your example:
Since angles between your 3 angles are both the same (11), you can just pick the middle bearing, recalculate it to absolute bearing by adding your course (Co) and add 90 degrees, which is 436 (-360 = 76)
If your angles are the same, course is logically perpendicular.

Don't forget that if the target would be moving to the left, you would be subtracting.

[Rosco74]

Very interesting thanks

[Xall]

Hey Palmic, I went to revisit this method, but the links to your cheat sheets are down, would you be so kind and upload them again? : )